It is known that firearms that have purely mechanical automatic trigger mechanisms, such as the type disclosed in U.S. Pat. No. 3,045,555 to Stoner, can operate with excessively high firing rates in an automatic firing mode. M16 type firearms using purely mechanical automatic trigger mechanisms can have rates of fire well in excess of 600 rounds per minute, particularly in models with shorter barrels. These high rates of fire may be problematic, as they can, among other things, affect the control and accuracy of the firearm, increase the accumulation of heat in the barrel, or result in unnecessary wastage of ammunition.
High rates of fire affect the control and accuracy of the firearm due to muzzle climb, as there is insufficient time between consecutive discharges to allow the operator to return the firearm to its original point of aim. This is compounded by a desire to increase the portability and maneuverability of firearms by reducing weight and size, which respectively contribute to decreased stability and further increased rates of fire.
In addition, the accumulation of heat in the barrel may contribute to erosion and wear in the barrel, and can further impact the accuracy of the firearm.
It is, therefore, desirable to provide an electro-mechanical trigger mechanism for an automatic firearm to provide a controlled rate of fire when the firearm is operated in an automatic firing mode.